Gas Processing Journal
Volume:1 Issue: 2, Spring 2013

In this work, the kinetics of ethane hydrate formation has been studied experimentally and a kinetic model based on chemical affinity has been described for predicting the hydrate growth process in the stirred batch reactor at a constant volume. The experiments were done with both pure water and aqueous solution of sodium dodecyl sulfate (SDS). The effect of SDS on formation kinetics has been investigated in concentrations: 300, 500 and 1000 PPM at different temperatures: 273.15, 274.15, 275.15 and 276.15 K. Experimental results showed the use of SDS decreases surface tension between the liquid and gas, then the ethane hydrate formation rate is increased, especially in SDS concentration of 500 PPM. The parameters of the model, Ar/RT and tK, were optimized for each experiment. The parameter Ar/RT was obtained a constant value for ethane gas. Acceptable agreement between the experimental and predicted data was generally found, and this model can sufficiently predict the formation pressure.

Minimizing the work consumed in refrigeration system is the most effective measure to reduce the cost of products in sub-ambient chemical processes. The introduction of mixed working fluids into refrigeration system in place of pure working fluids is a recent advancement applied in the field. Due to the lack of systematic design method for Mixed Refrigerant Cycle (MRC), conventional approaches are largely trialand- error, and therefore, operations might be far away from Optimal operating conditions. In this paper, a novel method for systematic design of MRCs with a given configuration is presented. It combines the benefits of thermodynamics approach and mathematical optimization. An ethylene process was chosen as a typical example of low temperature process. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system in the case of using Optimal operating conditions and also proper arrangement of the cycle components (cycle configuration).

In this study adiffusion based mathematical model was developed to compare the performance of amine-grafted adsorbents with that of 13X zeolite in a fixed-bed adsorption tower which is used to capture CO2 from both humid and dry nitrogen stream under industrial conditions. The results show that the performance of amine-grafted adsorbent and 13X zeolite is almost the same in the dry conditions. However, amine grafted adsorbents show better outcome when the gas stream is humid. Using amine-grafted adsorbents can reduce the expenses as a result of eliminating the pre-drying unit. Also the results of this simulation indicate that the economical breakthrough time is less than 30 minutes. This breakthrough time indicates that traditional TSA (Thermal Swing Adsorption) processes are uneconomical for regeneration of the adsorbents. Thus, a modified version of TSA process with lower regeneration time, i.e. RTSA (Rapid Thermal Swing Adsorption), must be employed for this case.

In this paper, Artificial Neural Network (ANN) was used for modeling the nonlinear structure of a debutanizer column in a refinery gas process plant. The actual input-output data of the system were measured in order to be used for system identification based on root mean square error (RMSE) minimization approach. It was shown that the designed recurrent neural network is able to precisely predict and track the response of the actual system. The comparison between the results of this paper and those of the most recent published studies as NARX model indicates the significance of the proposed approach.

In this study, the change in the crystalline structure of gas hydrate was predicted for ternary mixture of methane-ethane-water. For this purpose, the tangent plane distance (TPD) minimization method was used. First, the calculations were performed for the binary mixtures of methane-water and ethane-water as the gas and liquid phases. The results show that for a binary mixture of these components in the gas phase, at the temperatures of 274 K and 275 K, for a wide range of pressure, the phase remains stable; however, the liquid phase is unstable and it splits into two or more new phases. The method was used for any possible new phases and the stable new phases determined by TPD minimization. By using this method for the ternary mixture at 20 different points (pressure and composition) at the temperature of 277.6 K, the results for stable phases are found to be consistent with the literature; further, a structural change from sI to sII is observed at methane mole fraction of 0.74, and another structural change from sII to sI is observed at methane mole fraction of 0.99 at 277.6 K. This method can be used for the stability analysis of more points to predict the boundary of the phase diagram and stable zone for different phases. In this study, the genetic algorithm was used for minimization of TPD function.

In this paper, an exergy analysis approach is proposed for optimal design of distillation column by using simulated annealing algorithm. First, the simulation of a distillation column was performed by using the shortcut results and irreversibility in each tray was obtained. The area beneath the exergy loss profile was used as Irreversibility Index in the whole column. Then, First Optimization Algorithm (simulated annealing, SA) was implemented to Grassroots (Number of tray (N) vs. Reflux Ratio (RR)) and Retrofit (Nof vs. Feed splitting) cases, respectively. Next, SA was used to find the maximum recovery in a simple column by seven different variables (Feed Temperature, Feed Pressure, Reflux Rate, Number of theoretical stage, Feed Trays (Feed Splitting, three variables)) simultaneously. During the search for maximum recovery, it was tried to find a better Irreversibility Index. In the second part, SA optimization algorithm was used for a complex column with one pump-around and feed splitter to find a better condition, which means to find the best location for pump-around and feed trays in Distillation column. The main objective in SA was to maximize the recovery of the desired component and to find a better minimum Irreversibility Index. This method was implemented in de-ethanizer; in the first optimization without using pump-around with seven degrees of freedom, Recovery growth was 5.1% and reduction in irreversibility index was 3%. At the best Irreversibility Index, growth of recovery was about 3.7% and irreversibility index reduction was 25%. In the second optimization with pump-around or eight different variables, in the best condition, Recovery Growth was 6.2% but had a very high Irreversibility Index. At the best irreversibility index, recovery reduction was 17% but reduction in irreversibility index was about 21% comparing with initial point. As a result, it is shown that, regarding recovery and Irreversibility, pump-around shouldn
t be used in a column. Without using pumparound, a better condition, considering both factors, can be achieved.